Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. For example, SCS techniques, which stimulate the spinal cord tissue of the patient, have long been accepted as a therapeutic modality for the treatment of chronic neuropathic pain syndromes, and the application of (SCS) has expanded to include additional applications, such as angina pectoralis, peripheral vascular disease, and incontinence, among others. SCS is also a promising option for patients suffering from motor disorders, such as Parkinson's Disease, Dystonia and essential tremor.
An implantable SCS system typically includes one or more electrode-carrying stimulation leads, which are implanted at a stimulation site in proximity to the spinal cord tissue of the patient, and a neurostimulator implanted remotely from the stimulation site, but coupled either directly to the stimulation lead(s) or indirectly to the stimulation lead(s) via lead extension(s). The neurostimulation system may further include a handheld patient programmer to remotely instruct the neurostimulator to generate electrical stimulation pulses in accordance with selected neuromodulation parameters. The handheld programmer may, itself, be programmed by a technician attending the patient, for example, by using a Clinician's Programmer (CP), which typically includes a general purpose computer, such as a laptop, with a programming software package installed thereon.
Thus, programmed electrical pulses can be delivered from the neurostimulator to the stimulation electrode(s) to stimulate or activate a volume of the spinal cord tissue. In particular, electrical stimulation energy conveyed to the electrodes creates an electrical field, which, when strong enough, depolarizes (or “stimulates”) the neural fibers within the spinal cord beyond a threshold level, thereby inducing the firing of action potentials (APs) that propagate along the neural fibers to provide the desired efficacious therapy to the patient.
As discussed, SCS may be utilized to treat patients suffering from chronic neuropathic pain. To this end, mid- to high-frequency electrical stimulation is generally applied to the sensory afferents of the dorsal column (DC) nerve fibers at an amplitude that creates a relatively comfortable sensation of paresthesia. While the full mechanisms are pain relief are not well understood, it is believed that the perception of pain signals is inhibited via the gate control theory of pain, which suggests that enhanced activity of innocuous touch or pressure afferents via electrical stimulation creates interneuronal activity within the dorsal horn that releases inhibitory neurotransmitters (e.g., Gamma-Aminobutyric Acid (GABA), glycine), which in turn, reduces the hypersensitivity of wide dynamic range (WDR) sensory neurons to noxious afferent input of pain signals traveling from the dorsal root (DR) neural fibers that innervate the pain region of the patient, as well as treating general WDR ectopy. Consequently, stimulation electrodes are typically implanted within the dorsal epidural space to provide stimulation to the DC nerve fibers.
Although it would be desirable to epidurally stimulate DC nerve fibers, various sensitive neural structures, including the DR and ventral root (VR) nerve fibers, are in close proximity to DC nerve fibers. As a result, SCS stimulation to treat chronic neuropathic pain may be difficult to accomplish without also inadvertently creating side-effects, e.g., in the form of uncomfortable muscle contractions and pain resulting from the inadvertent activation of the VR nerve fibers, either by reflex (via DR stimulation) or by direct VR stimulation, or both. There, thus, remains a need to minimize activation of efferent neural structures, while stimulating or at least modulating afferent neural structures.
Alongside the neuropathic pain (typically well-treated by SCS), patients may also experience nociceptive pain, resulting from nerve impingement or inflammation. In such instances, the nociceptive pain is rarely useful for protection or survival and thus could be dispensed with. Opioids are often used to manage nociceptive pain, but they can have significant side effects when taken chronically and systemically. Interventional procedures using ablation can be effective, but are necessarily destructive and may have undesirable sequelae. Other interventions using local steroids or anesthetics can be very effective, but require accurate needle placement by a physician. Acupuncture is another method for treating nociceptive pain as is low frequency/high intensity Transcutaneous Electrical Nerve Stimulation (TENS). Both of these treatments engender an endogenous opioid release ostensibly by mild activation of low threshold pain afferents (A-delta nerve fibers). Acupuncture typically requires a specialist for needle placement and can be inconvenient. Low frequency/high intensity TENS can also be inconvenient, requiring skin patch applications. There, thus, remains a need for a convenient stimulation procedure that would ameliorate nociceptive pain.